编组结构时间的通用方法.使用自定义格式将时间字段转换为JSON [英] Generic approach for marshalling a struct's time.Time fields to JSON with custom formatting

问题描述

我的数据模型定义了多个结构，它们都具有两个共同的字段:StartDate和EndDate.我需要将这两个字段在经过编组的JSON中格式化为2018-09-21，因此结构实现了Marshaller接口:

My data model defines multiple structs that all have two fields in common: a StartDate and an EndDate. I need those two fields to be formatted as 2018-09-21 in the marshalled JSON, therefore the structs implement the Marshaller interface:

type Results struct {
    Source     string    `json:"source"`
    StartDate  time.Time 
    EndDate    time.Time 
}

type WeightedResults struct {
    Source          string           `json:"source"`
    StartDate       time.Time        
    EndDate         time.Time        
}

func (r Results) MarshalJSON() ([]byte, error) {
    type Alias Results
    if equalDate(r.StartDate, r.EndDate) {
        return json.Marshal(&struct {
            Date string `json:"date"`
            Alias
        }{
            Date:  r.StartDate.Format(dateFormat),
            Alias: (Alias)(r),
        })
    }    
    return json.Marshal(&struct {
        StartDate string `json:"start_date"`
        EndDate   string `json:"end_date"`
        Alias
    }{
        StartDate: r.StartDate.Format("2006-01-02"),
        EndDate:   r.EndDate.Format("2006-01-02"),
        Alias:     (Alias)(r),
    })
}

func (r WeightedResults) MarshalJSON() ([]byte, error) {
    type Alias WeightedResults
    if equalDate(r.StartDate, r.EndDate) {
        return json.Marshal(&struct {
            Date string `json:"date"`
            Alias
        }{
            Date:  r.StartDate.Format(dateFormat),
            Alias: (Alias)(r),
        })
    } 
    return json.Marshal(&struct {
        StartDate string `json:"start_date"`
        EndDate   string `json:"end_date"`
        Alias
    }{
        StartDate: r.StartDate.Format("2006-01-02"),
        EndDate:   r.EndDate.Format("2006-01-02"),
        Alias:     (Alias)(r),
    })
}

上面的解决方案可以正常工作，但是会产生大量的代码重复.有什么方法可以重构MarshalJSON的两个实现以使用相同的逻辑/代码?我很清楚Go还没有提供泛型，但是必须解决这个问题，对吗?

The solution above works fine but yields lots of code duplication. Is there any way to refactor both implementations of MarshalJSON to use the same logic/code? I am well aware that Go does not offer Generics (yet), but there has to be another way around this issue, right?

推荐答案

您的自定义封送拆封器不应位于结构上，而应位于嵌入time.Time的自定义类型上:

Your custom marshaler should not be on the structs, but on a custom type that embeds time.Time:

type MyTime struct {
    time.Time
}

func (t MyTime) MarshalJSON() ([]byte, error) {
    return json.Marshal(t.Format("2006-01-02"))
}

然后在您想要的任何地方使用此类型.

Then use this type everywhere you want.

type Results struct {
    Source     string    `json:"source"`
    StartDate  MyTime
    EndDate    MyTime
}

这篇关于编组结构时间的通用方法.使用自定义格式将时间字段转换为JSON的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！